1. Field of the Invention
The present invention relates to a constant-pressure air-storage cavern with hydraulic pressure compensation for air-storage gas turbine power stations in accordance with the pre-characterizing clause of claim 1.
2. Description of the Prior Art
In comparison with air-storage systems with variable air pressure which, in operation, is allowed to fluctuate within certain limits, and having an efficiency which is equal to that of constant-pressure air-storage systems for gas turbine power stations, the latter require only about a third of the volume of the former. Accordingly, the constructional effort and building costs for a cavern intended for constant-pressure storage are much less than for caverns intended for variable air pressure.
In order to maintain the air pressure constant in a constant-pressure storage system, a water seal is used which equalizes the volume of air consumed in the cavern and which is provided with a water column which opens into a free basin usually located at the surface of the earth and the static pressure head of which corresponds to the pressure to be maintained in the cavern. When the cavern, which in present-day installations is located at a depth of 600-800 m, corresponding to a static pressure of the water column of 60-80 bar, is charged the water is forced up into the basin and when the cavern is discharged the water flows from the basin back into the cavern in order to ensure that the pressure is the same.
In order to make it possible to alternately charge and discharge the storage cavern, shut-off elements, which must be appropriately actuated during the transition from charging to discharging operation and vice versa, are located between the air duct rising from the cavern and the compressor, on the one hand, and, on the other hand, in front of the combustion chamber of the turbine. If this change-over is not carried out correctly, for example if such accidentally remains wholly or partially open, or if a pipe leakage or a fault in the compressor blading occurs, the compressed air can escape from the cavern which causes the water in the cavern to rise. If the wrong operation of the abovementioned shut-off elements is not instantly corrected or the pipe leakage cannot be eliminated in the most rapid manner, the danger exists that, as a result of the gas evolution in the air duct because of the decrease in hydrostatic pressure, with a corresponding increase in the volume of the water/air mixture, the water will race up into the turbine plant which may have devastating consequences for the whole plant.
The suggestions which have hitherto become known for solving this problem are based on various principles. Some are based on shielding the water surface as completely as possible against contact with air and thus preventing the absorption of air in the water. This is associated with floatable mechanical means for covering the water such as floats carried on vertical rods, tarpaulins with bouyancy bodies, floating balls and similar means and covering layers, which float on the water, of a liquid with lighter specific gravity than water. Other suggestions have the object of preventing the bubbles forming in the water seal from rising into the basin above ground, the equalizing basin. The means used for this purpose include, for example, risers which open into the environment above the water level of the equalizing basin, turbine wheels which are intended to separate out small air bubbles before critical bubble formation occurs, and other mechanical measures which are in some cases very elaborate.
None of these suggestions are wholly satifactory in practice since they are constructionally elaborate and also not completely maintenance-free. In addition, their effectiveness has not been tested in practice and is thus still unproven.